Transducers



L. J. BOBB TRANSDUCERS June 16, 1959 2 Sheets-Sheet 1 Filed Aug 16, 1956NEE IN V EN TOR. a am A 5055 muwr L. J. BOBB TRANSDUCERS June 16, 1959 2Sheets-Sheet 2 Filed Aug. 16, 1956 INVENTOR. [10/0 4/ 19055 UnitedStates Patent() TRANSDUCERS Lloyd J. Bobb, Glenside, Pa., assignor toPhilco Corporation, Philadelphia, Pa., a corporation of PennsylvaniaApplication August 16, 1956, Serial No. 604,377

2 Claims. (Cl. 181-31) This disclosure has to do with the art ofreproducing sound, such as music and speech. It relates particularly toloud-speakers such as those of broadcast receivers, phonographs, and thelike, for carrying reproduced speech or music, by direct acousticaltransmission, to a number of persons, constituting an audience. Morespecifically, the invention is concerned with a diaphragm of novel,characteristic form, in or for a dynamic speaker.

Heretofore dynamic speakers generally had diaphragms of conical shapewith circular base, although sporadically, speakers of modified formswere used or proposed. The modified shapes included cones of oval base,pyramids, etc., which were considered for a variety of reasons,including for instance the idea that the working area or vibratingportion of a cone could be increased by integral reinforcement features.However, matters such as the provision of a large area for directradiation are only some of the many and complex elements of eflicientspeaker performance; and the overall performance was not greatlyimproved by the prior constructions modifying the circular cone, or wassometimes even impaired thereby.

It is known that in the lower octaves of acoustical work the conicalspeaker of circular base is generally adequate and that the problem inthe higher octaves is complicated by narrowness of directive pattern,rather than insufliciency of radiating area. For this reason muchconsideration was given to designs wherein conventional dynamic speakerswith circular cones Were combined with special horn structures or bafilestructures, having long and narrow mouth sections; and when broaddiffusion over a large horizontal area was desired the narrow and elongated mouth section was vertically arranged. The narrowness of such asection caused improved average dilfusion of high frequency sound,transversely of the slot, while the elongation of the slot was relied onto insure adequate average emission of medium and low frequency sound.However, the acoustical power output of a speaker, provided by a givennumber of watts or fractional watts of electrical power input, wasgreatly reduced, mainly in the low and medium frequencies, by theacoustical resistance of the air confined between the wide, vibratingdiaphragm and the narrowly apertured bafile or horn. In addition theever-present dangers of sound distortion were increased as the bafflesor horns, the material thereof and the air enclosed thereby introducednew disturbing possibilities of specific resonance, damping and thelike; the speaker diaphragm no longer radiated the sound directly to theaudience.

It is now usual to combine two or more speakers of different type, forinstance so-called woofers and tweeters, whenever it is desired toreproduce sound with low distortion for any audience. However, theprovision and matching of such speakers is not only expensive andspace-consuming but is also conducive to further acousticaldifficulties. For instance the cost and space requirements areapproximately doubled whentwo speakersare 2,890,760 Patented June 16,1959 used, one as a so-called woofer and one as a so-called tweeter; andin addition it becomes necessary to arrange for a so-called cutting offand matching of frequency response characteristics of the two speakers,incident to which irregularities of response curves of the two speak ersmay be intensified in that portion of the complete frequency range wherethe one curve tapers off and the other rises.

It has occurred to me, and accordingly forms an object of my presentinvention, to construct a single-source, direct-radiating, high-fidelitysound generator; that is, a speaker which not only provides adequateemission of all sound, including that of low frequency and broaddiffusion of all sound, including that of high frequency, but alsoavoids such troubles as those caused either by in-' direct radiationthrough a partially enclosed air space or by the cost, space andmatching problems of speaker sys-' tems with more than one kind ofspeaker. The new type of speaker basically involves the use of a singlemotordriven loud-speaker diaphragm having a novel and characteristic,elongated and narrow form which resembles the form of a small boat.According to this idea, then, there may be used an outline approximatingthose which were usedas the forms of a mouth section in some of theprevious constructions; but according to my new idea I the long andnarrow outline in question defines the form taper off toward narrowerends 14. Thus the diaphragm.

of anentire direct-radiating speaker, and no structure confining anarrow air space need be used in front of the speaker.

It has actually be found that acoustical results improved over those ofprior single speakers can thus be achieved; there can be used fewerparts and cheaper constructions than are required by the more complexhighfidelity systems, with two or more than two types of speakers; andthe performance of the new single speaker can often be at least as goodas, or better than, that of the systems with two types of speakers,while being muchcheaper and simpler and more compact. In addition, thedesign of cabinets and the like, associated with loudspeakers, has beenimproved by certain applications of these devices.

The improvements of cabinet design and the like as well as the novelacoustical features of the new speaker, will now be explained inconjunction-with the drawing appended hereto, wherein Figures 1 and 2are front and side views,'respectively, of a preferred embodiment of thenew diaphragm, and Figure 3 is an enlarged section through the same, thesection being taken along line 3-3 in Figure 2.

Figure 4 is a perspective exploded view of a loud-.: speaker comprisingthe new diaphragm, and

Figures 5 and 6 are diagrammatic sketches showing respectively atelevision cabinet and the rear parcel shelf of an automobile, bothhaving typical embodiments of the body 10, having the approximate shapeof a miniature boat. Usually the diaphragm has, as shown,a marginal,outwardly extending, corrugated, desirably integral collar 11.

A central portion of the diaphragm may have a small,

desirably circular neck 12, desirably extending toward the.

convex side; and this neck may be covered by an elongated dust shield13. The diameter of the neck is somewhat smaller than the width of theadjacent parts of the diaphragm; and said width of the diaphragm isapproximately uniform over a substantial, inner part of its length, butthis width as well as the height of'the diaphragm may may also becompared with a two-armed, outwardly tapering trough or channel with acentral header or collector.

The width of the new diaphragm is a feature of paramount importanceparticularly in connection with the diffusion of high frequency soundradiation. While this width may differ to a limited extent, dependingupon the specific use for which a particular embodiment of the newdiaphragm may be intended, the new diaphragm is always considerablynarrower than any of the diaphragms which previously were used or builtin forms adapted to be used for comparable purposes. Allowablevariations of the width of the new diaphragm are not dictated byconsiderations of acoustical power, which was the controlling factor forthe dimensioning of prior forms of diaphragms but by consideration suchas: use of the diaphragm for the reproduction of speech or of music, andmounting of the speaker in front of a wide wall or in the corner of aroom. The mentioned forms of mounting call for diffusion of the varioussounds in patterns of different angularities; and the different types ofsound to be reproduced involve somewhat different problems of diffusion,since the highest important frequencies, including the most importantovertones, range up to about 4,000 or 5,000 cycles per second in thecase of spoken sound, whereas they range considerably higher in mostcases of musical reproduction. Correspondingly the width of the newdiaphragm should be limited in manners which will readily be understoodby persons skilled in the art in the light of the disclosure givenherein. For in stance if the speaker serves to reproduce human speechonly, it can often be made about two or three inches wide; if a widerange of musical sounds shall be reproduced with low distortion, it ispreferable to make the speaker only about one inch wide and in somecases to mount it in a corner.

While diffusion of sound is thus benefited by narrowness of thediaphragm, it is generally undesirable to reduce the width of thediaphragm beyond certain lowermost limits, such as about three-quartersof an inch, or for practical purposes, about one inch; these valuesbeing smaller than one-half the wavelengths of the highest fundamentalmusical sounds and being equal to one-half the wavelengths of the mostimportant harmonics. This relationship between width of the diaphragmand halfwavelength of the highest significant sounds emitted has beenfound to be controlling. Any further reduction of the width of thediaphragm would gain no further, practical advantage with respect todiffusion of sounds re quired for undistorted reproduction, whereas itwould lead to new difliculties, such as specific resonance and impairedamplitude, the latter mainly in the bass register; and these phenomenacan be, generally speaking, as critical and as damaging as anunsatisfactory directional pattern.

In order to insure acoustical amplitude or power, the new diaphragm hasnot only a positive although limited width, as just explained, but alsosubstantial elongation. Thus it is a principal function of theelongation of the diaphragm to insure adequate air coupling-a featurewhich is known to be important mainly in the lower and medium ranges ofspoken and musical sounds. However, important limitations are againencountered: the elongation of the diaphragm must not be driven to thepoint where the unit resembles a string or the like, having a preferredfrequency of its own and disturbing the frequency response of the unit.Practically, I found it most advantageous to provide the diaphragms ofthis invention with a length of about five to seven times the aforesaidwidth, preferably using a length to Width ratio or aspect ratio of about7:1 for the narrowest diaphragms of about one inch width, and aspectratios ranging between 5:1 and 7:1 for the wider diaphragms, of abouttwo to three inches in width. Thus a radiating area of about sevensquare inches is provided in the case of a diaphragm of one inch width,and either proportionately or almost 4 proportionately more in the caseof the relatively wider diaphragms. Of course a plurality of the newdiaphragms can be used together, with proper precautions of generallyknown kind; and such a combination can be and is considered as basicallya single source of sound, it being unnecessary to combine differentvariants of the new diaphragm, such as woofers and tweeters. Thecombining, if any, of several units of the new speaker will usually belimited to the building up of greater acoustical power.

The height of the diaphragm, measured between the collar 11 and neck 12,is desirably made as small as or even smaller than the aforementionedwidth, in order to maintain the high frequency diffusion and to avoidbreaking down of the frequency response curve. Such breaking down isotherwise caused by an excessive degree of longitudinal reinforcement ofthe diaphragm, a reinforcement efiect being inherent in the boatshapedor troughshaped design and particularly in the use of longitudinal wallsections as part of this design.

The volume and other characteristics of sound emitted by the newdiaphragm are as satisfactory as those of a circular conical diaphragmof equal area, whereas the direcive patterns are widened and thefrequency response obtained in the outer portion of the sound radiationarea is improved. The improvements are substantial and they can beattributed entirely to the combined features of a diaphragm widthabsolutely limited to the range from about one to about three inches anda diaphragm length limited to the range of about five to about seventimes this width. The improvements are independent of the diaphragmmaterial, the electrical power source and other similar factors: thesecan be the same as in ordinary dynamic speaker cones.

The criticality of the combined features of aspect ratio and width isunique to the new form of diaphragm. For instance there is no suchcriticality of dimensions in any of the circular cone-shaped speakerdiaphragms known to the art; on the contrary, any attempt to reducetheir width or diameter to anything like one or three inches or a halfor full wavelength of a typical high sound would make those knowndiaphragms entirely too small and feeble to radiate low and mediumsounds so as to reach a plurality of listeners and thus to serve asloud-speakers at all. There is not even any close similarity between theperformance of the present loud-speaker and that of the known, circularcone speaker with a narrow horn or narrowly slotted bafile in front,when using identical forms and sizes for the slot in the baffle of saidspeaker and for the new speaker, and identical operating conditions inall other respects; there is, on the contrary, a perplexing multiplicityof differences in details of the respective performances, mainly withrespect to frequence response, and of course, as mentioned, with respectto acoustical output.

It will be seen, in summary, that the invention may be defined iascomprising or including a vibratory diaphragm of long, narrow designwhich may be generally oval and which should have no more than aboutthree, inches and desirably only about one inch width, having similar orsmaller depth and having a length of several times the said width; thevibratory diaphragm having a continuously curved boat-likecross-sectional shape (see Figure 3), thereby avoiding the use ofstraight-lined and cornered portions. The use of such portions, asmentioned, would cause acoustic disadvantages because of excessivereinforcement of the vibratory diaphragm, as was the case in said priorspeakers constructed with pyramid-shaped diaphragm elements.

The mounting of the new diaphragm, as shown in Figure 4, can be verysimple. The peripheral part of the collar 11 may be fastened, forinstance by cementing, to the corresponding part of a flange structure15 forming part of a bridge 16, whereas the neck 12 may be flexiblysecured to the center part of the bridge by a small collar 17. Centrallyof this small collar, a suitable acoustical motor 18 is installed, forinstance a dynamic voice coil unit, the details of which need not beexplained herein since they may be conventional. The coil or equivalentpart of this unit is directly or indirectly secured, in known manner, tothe diaphragm neck 12. The flange may provide for mounting screws 19 orthe like, for attaching the entire periphery of the loudspeaker to apanel or the like, not shown, with a resilient gasket 20 interposedbetween the flange structure and the panel and an acousticallytransparent cover 21, such as a sheet of fabric and/or system of fretwork, secured to the mouth of the speaker.

As further shown in Figure 5, the mounting panel 22 of a singleloud-speaker according to this invention may constitute one of thevertical sides of the front panel of a television receiver; in otherwords, it may practically fill the narrow, vertical area provided insuch a receiver, between the screen 23 and one side edge of the cabinet.The speaker motor can be powered by the single speaker output (notshown) of a relatively simple TV set, as usual. This construction isfacilitated by the fact that the aforementioned longitudinal dimensionsof a speaker according to this invention, ranging approximately betweenseven inches and twenty-one inches, happen to agree admirably with suchvertical dimensions of direct-viewing TV receiver screens as have beenfound most favorable, in the development of such screens. At the sametime the extreme narrowness of the new speaker, often involving onlyabout one or two and generally not more than three inches, has theeffect that no costly, lateral enlargement of the cabinet and woodworkis required. No more than one speaker is usually required, even wherethe standards for acoustical quality are quite high; thus the aforesaidproblems, such as those of the matching of plural speakers, of differentkind, are avoided by the new speaker design.

The characteristic form of the new speaker provides acoustical as wellas structural advantages in a number of other instances, where soundreproducers are built into cabinets or other units which must fitlimited dimensions of other equipment and which, nevertheless, mustserve the acoustical needs of relatively large spaces. As one furtherexample, Figure 6 shows a sectional view of the rear parcel shelf 24 inan automobile 25, with a speaker 16 according to the present inventioninstalled on the underside of this shelf, the elongated diaphragmextending transversely of the car. The speaker motor is normallyconnected with the automotive radio set, not shown. The quality of thereception of music which may be enjoyed by the different occupants ofthe car,

in motion as well as at rest, is greatly improved by this design. In thepresent case, much of the sound emitted by the speaker reaches thelisteners by reflection from the top of the car; but Whether the soundbe received with or without reflex, the important point is that theentire range of frequencies is uniformly distributed to the entire spacebetween the speaker and a number of listeners.

While only a single embodiment of the diaphragm and speaker and twotypes of mounting thereof have been described, it should be understoodthat the details of the description and illustration are not to beconstrued as limitative of the invention, except insofar as set forth inthe following claims.

I claim:

1. In apparatus for reproducing speech and musical sound and forefliciently diffusing the reproduced sound throughout a wide listeningarea, a diaphragm unit comprising: a vibratory diaphragm, having thegeneral shape of a long, narrow boat, the width thereof being no greaterthan about three inches, the length thereof being of the order of atleast approximately five times said width, and the shape thereof beingsubstantially smoothly curved in cross section; a diaphragm neck, formedin central position on said diaphragm, for connection to an acousticmotor; and a diaphragm collar, formed in peripheral position on saiddiaphragm, for connection to a structure supporting the diaphragm at onelocation in said wide listening area.

2. Apparatus for generating and widely diffusing audible sound,comprising: a vibratory diaphragm, having the general shape of a long,narrow boat, substantially no Wider than one-half of the shortestwavelength of said sound, the length of the vibratory diaphragm being ofthe order of at least approximately five times the width thereof, andthe shape of the vibratory diaphragm being substantially smoothly curvedin cross section; a diaphragm neck and acoustic motor structure,connected to a central portion of said vibratory diaphragm; and a.collar, formed in peripheral position on said vibratory diaphragm, forconnection of the diaphragm to a support structure.

References Cited in the file of this patent UNITED STATES PATENTS1,819,627 Staunton Aug. 18, 1931 1,930,328 Tichenor et al. Oct. 10, 19332,350,889 Harman June 6, 1944 2,470,620 Jackson May 17, 1949

